An Update on UV LED Screen Exposure

Every technical support person in the industry has at least one anecdote of a mysterious quality-control problem that was eventually traced to the exposure unit sitting in the corner of the screenroom. My favorite involves a shop that suddenly began experiencing screen breakdown during its production runs. The technician checked the ink and press parameters to see if something was attacking the stencils. She looked into QC records from the emulsion manufacturer, the coating procedures in the shop, and the exposure unit’s functionality and could find no explanation.

Finally, the technician asked the worker who exposed the screens if he was doing anything differently. No, he explained: Each time he exposed a screen, he turned the unit on, lit a cigarette, and stopped the unit when he was finished smoking, knowing the screen would be finished. The punch line is that he had recently switched cigarette brands and the new one burned more quickly, so all of the screens he was producing were underexposed.

I suspect that few other shops used the “Marlboro method” to calculate exposure times, but the story illustrates how little attention has traditionally been paid to a process that can cause a myriad of production and quality problems when it isn’t done correctly. As screen printers adapt to the realities of falling run lengths, faster turnaround times, and narrower margins, they can’t afford such bottlenecks and errors in their prepress any longer.

Recently, screen exposure has become a very active topic due to the emergence of a new class of exposure systems employing a light source that has become ubiquitous in many facets of our lives—LEDs (light-emitting diodes). Exposure systems powered by UV LEDs began hitting the market in 2013 and have quickly attracted a lot of attention, particularly among garment printers. They offer several tantalizing advantages over conventional light sources and the potential to streamline prepress workflow. Not surprisingly, they have also prompted some questions among potential users and more than a little debate between technology developers.